Method and system for adjusting a fuel tank isolation valve

ABSTRACT

Methods and systems are provided for adjusting and diagnosing a position of a fuel tank isolation valve of a fuel system. In one example, a method may include adjusting the fuel tank isolation valve via electrical pulses and tracking a position of the FTIV by counting each of the electrical pulses. When a vacuum is created in the fuel system, the method may include verifying the position of the FTIV based on resulting fuel system pressures.

BACKGROUND/SUMMARY

Vehicle emission control systems may be configured to store fuel vaporsfrom fuel tank refueling and diurnal engine operations, and then purgethe stored vapors during a subsequent engine operation. In hybridvehicles, shorter engine operation times can lead to insufficientpurging of fuel vapors from the vehicle's emission control system. Toaddress this issue, hybrid vehicles may include a fuel tank isolationvalve (FTIV) between a fuel tank and a hydrocarbon canister of theemission system to limit the amount of fuel vapors absorbed in thecanister. In some examples, the FTIV may be a bi-stable valve adjustablebetween open and closed positions via a short electrical pulse. However,a position of the FTIV during use may not be known without an additionalsensor. As a result, the FTIV may be adjusted into a different positionthan desired during operation.

One example approach of a bi-stable isolation valve is shown by Takagiet al. in U.S. Pat. No. 6,761,154. Therein, an electromagneticallyactuated open/close valve is shown in a vapor passage between a fueltank and a fuel canister. The valve is opened and closed under differentengine operating conditions; however, there may not be a way ofdiagnosing a position of the valve.

As one example, the issues described above may be addressed by a methodfor adjusting a fuel tank isolation valve (FTIV) of a fuel system bysending electrical pulses to the FTIV, counting each of the electricalpulses to track a position of the FTIV, and verifying the position ofthe FTIV when a vacuum is created in the fuel system. In this way, theposition of the FTIV may be diagnosed, thereby resulting in increasedaccuracy of subsequent valve control.

For example, when a vacuum (e.g., fuel system pressure below a vacuumthreshold pressure) is sensed in the fuel system, the FTIV must beclosed otherwise the vacuum may not be achieved. Thus, verifying theposition of the FTIV may include verifying the FTIV is closed when avacuum is sensed in the fuel system. Additionally or alternatively, theFTIV may be verified as closed responsive to a fuel tank pressuregreater than a threshold pressure. A vacuum may be applied to the fuelsystem in response to the position of the FTIV being unknown, a durationsince last diagnosing the FTIV position, and/or a request to run a leakcheck routine in the fuel system. In one example, a controller mayoperate a vacuum pump of an evaporative leak check module (ELCM) inorder to apply the vacuum to the fuel system. If no vacuum is sensedafter applying the vacuum to the fuel system, the controller maydetermine the FTIV is open.

After diagnosing the position of the FTIV, the controller may adjust theFTIV into a desired position. In one example, adjusting the FTIV to thedesired position includes sending an electrical pulse to actuate theFTIV from a first position to the desired position. In another example,adjusting the FTIV to the desired position may include not sending theelectrical pulse to actuate the FTIV when the FTIV is already in thedesired position. In some examples, degradation of the FTIV may also bedetermined if the FTIV is verified as being open when it is supposed tobe closed. Thus, as a result of applying a vacuum to the fuel system,the position of the FTIV may be determined and used for subsequent valvecontrol.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic depiction of an example fuel system of avehicle.

FIG. 2 shows a detailed embodiment of the fuel system of FIG. 1.

FIG. 3 shows a flow chart of a method for adjusting a fuel tankisolation valve.

FIG. 4 shows a flow chart of a method for diagnosing a position of afuel tank isolation valve.

FIG. 5 shows a graphical example of adjustments to a fuel tank isolationvalve.

DETAILED DESCRIPTION

The following description relates to systems and methods for adjustingand diagnosing a position of a fuel tank isolation valve (FTIV) of afuel system, such as the fuel system shown in FIGS. 1-2. The FTIV may bepositioned between a fuel tank and a fuel canister of the fuel system.Additionally, the FTIV may be a bi-stable valve actuated between openand closed positions via a short electrical pulse sent by a controller.A method for adjusting the FTIV into the open or closed position, basedon the current or known valve position, is shown at FIG. 3. In somecases, the current position of the FTIV may not be known. In response tonot knowing the FTIV position, or after or period of valve operation,the controller may adjust a fuel system component and then verify theposition of the FTIV. In one example, a vacuum pump may be operated tocreate a vacuum in the fuel system. If the vacuum is successfullycreated, the FTIV may be verified as closed. However, if the vacuum isnot successfully created, the FTIV may be verified as open. Subsequentvalve control may then be based on the verified (e.g., known) position.A method for diagnosing the position of the FTIV and applying a vacuumto the fuel system is shown at FIG. 4. In alternate embodiments,additional or alternative fuel system components, such as a differentpump, may be adjusted to create a vacuum in the fuel system or increasefuel tank pressure above a threshold pressure. Example adjustments to aFTIV based on engine operating conditions and operation of a vacuum pumpare shown at FIG. 5.

FIG. 1 shows a schematic depiction of a hybrid vehicle system 6 that canderive propulsion power from engine system 8 and/or an on-board energystorage device, such as a battery system 52. An energy conversiondevice, such as a motor/generator 50, may be operated to absorb energyfrom vehicle motion and/or engine operation, and then convert theabsorbed energy to an energy form suitable for storage by the energystorage device.

Engine system 8 may include an engine 10 having a plurality of cylinders30. Engine 10 includes an engine intake 23 and an engine exhaust 25.Engine intake 23 includes a throttle 62 fluidly coupled to the engineintake manifold 44 via an intake passage 42. Engine exhaust 25 includesan exhaust manifold 48 leading to an exhaust passage 35 that routesexhaust gas to the atmosphere. Engine exhaust 25 may include one or moreemission control devices 70 mounted in a close-coupled position. The oneor more emission control devices may include a three-way catalyst, leanNOx trap, diesel particulate filter, oxidation catalyst, etc. It will beappreciated that other components may be included in the engine such asa variety of valves and sensors, as further elaborated at FIG. 2.

In some embodiments, engine intake 23 may further include a boostingdevice, such as a compressor 74. Compressor 74 may be configured to drawin intake air at atmospheric air pressure and boost it to a higherpressure. As such, the boosting device may be a compressor of aturbocharger, where the boosted air is introduced pre-throttle, or thecompressor of a supercharger, where the throttle is positioned beforethe boosting device. Using the boosted intake air, a boosted engineoperation may be performed.

Engine system 8 may be coupled to a fuel system 18. Fuel system 18 mayinclude a fuel tank 20 coupled to a fuel pump system 21 and one or more(one depicted in the present example) fuel vapor canisters 22. Fuel tank20 may hold a plurality of fuel blends, including fuel with a range ofalcohol concentrations, such as various gasoline-ethanol blends,including E10, E85, gasoline, etc., and combinations thereof. Fuel pumpsystem 21 may include one or more pumps for pressurizing fuel deliveredto the injectors of engine 10, such as example injector 66. While only asingle injector 66 is shown, additional injectors are provided for eachcylinder. It will be appreciated that fuel system 18 may be areturn-less fuel system, a return fuel system, or various other types offuel system. Vapors generated in fuel tank 20 may be routed to fuelvapor canister 22, described further below, via conduit 31, before beingpurged to the engine intake 23.

Fuel vapor canisters 22 may be filled with an appropriate adsorbent, fortemporarily trapping fuel vapors (including vaporized hydrocarbons)generated during fuel tank refueling operations, as well as diurnalvapors. In one example, the adsorbent used is activated charcoal. Whenpurging conditions are met, such as when the canister is saturated,vapors stored in fuel vapor canister (e.g., fuel vapor recovery system)22 may be purged to engine intake 23 via purge line 28 by openingcanister purge valve 112.

Canister 22 may be further coupled to a vent 27 which may route gasesout of the canister 22 to the atmosphere when storing, or trapping, fuelvapors from fuel tank 20. Vent 27 may also allow fresh air to be drawninto canister 22 when purging stored fuel vapors to engine intake 23 viapurge line 28 and purge valve 112. In some examples, a canister checkvalve 116 may be optionally included in purge line 28 to prevent(boosted) intake manifold pressure from flowing gases into the purgeline in the reverse direction. While this example shows vent 27communicating with fresh, unheated air, various modifications may alsobe used. A detailed configuration of fuel system 18 is described at FIG.2, including various additional components that may be included in theintake and exhaust.

As such, hybrid vehicle system 6 may have reduced engine operation timesdue to the vehicle being powered by engine system 8 during someconditions, and by energy storage device 52 or motor 50 under otherconditions. While the reduced engine operation times reduce overallcarbon emissions from the vehicle, they may also lead to insufficientpurging of fuel vapors from the vehicle's emission control system. Toaddress this, fuel tank 20 may be designed to withstand high fuel tankpressures. For example, fuel tank 20 may be constructed of material thatis able to structurally withstand high fuel tank pressures (such as fueltank pressures that are higher than a threshold and below atmosphericpressure).

Additionally, a fuel tank isolation valve (FTIV) 110 may be included inconduit 31 such that fuel tank 20 is coupled to the canister of fuelvapor recovery system 22 via the valve. Isolation valve 110 may be abi-stable solenoid valve wherein operation of the valve may be regulatedby adjusting a driving signal to (or pulse width of) the dedicatedsolenoid (not shown). Specifically, short electrical pulses may be sentto the isolation valve 110 to actuate the valve and switch a position ofthe valve (e.g., from open to closed or from closed to open). Bi-stablemeans that the isolation valve 110 may not a have a base position inwhich the valve is normally open or closed. For example, the bi-stableisolation valve 110 may require two signals to operate: one to open thevalve and one to close the valve. If system power is lost or the valvebecomes degraded, it may not switch back to a known position. Thus,there may not be a way of detecting the position of the isolation valve110 without an additional sensor.

In some cases, the isolation valve 110 may be kept closed to limit theamount of fuel vapors absorbed in the canister from the fuel tank 20.The closed isolation valve 110 thereby separates storage of refuelingvapors from the storage of diurnal vapors. The isolation valve 110 isopened during refueling to allow refueling vapors to be directed to thecanister. As another example, the closed isolation valve 110 may beopened during selected purging conditions, such as when the fuel tankpressure is higher than a threshold (e.g., a mechanical pressure limitof the fuel tank above which the fuel tank and other fuel systemcomponents may incur mechanical damage), to release fuel vapors into thecanister and maintain the fuel tank pressure below pressure limits. Theisolation valve 110 may also be closed during leak detection routines toisolate the fuel tank from the engine intake.

One or more pressure sensors (FIG. 2) may be coupled to the fuel tank,upstream and/or downstream of isolation valve 110, to estimate a fueltank pressure, or fuel tank vacuum level. One or more oxygen sensors(FIG. 2) may be coupled to the canister (e.g., downstream of thecanister), or positioned in the engine intake and/or engine exhaust, toprovide an estimate of a canister load (that is, an amount of fuelvapors stored in the canister). Based on the canister load, and furtherbased on engine operating conditions, such as engine speed-loadconditions, a purge flow rate may be determined.

Leak detection routines may be intermittently performed on fuel system18 to confirm that the fuel system is not degraded and/or diagnose aposition of the isolation valve 110. As such, leak detection routinesmay be performed while the engine is off (engine-off leak test) usingengine-off natural vacuum (EONV) generated due to a change intemperature and pressure at the fuel tank following engine shutdownand/or with vacuum supplemented from a vacuum pump. Alternatively, leakdetection routines may be performed while the engine is running byoperating a vacuum pump and/or using engine intake manifold vacuum. Leaktests may be performed by an evaporative leak check module (ELCM) 140communicatively coupled to controller 12. ELCM 140 may be coupled invent 27, between canister 22 and the atmosphere. As elaborated at FIG.2, ELCM 140 may include a vacuum pump for applying negative pressure tothe fuel system when administering a leak test. ELCM may further includea reference orifice and a pressure sensor. Following the applying ofvacuum to the fuel system, a change in pressure at the reference orifice(e.g., an absolute change or a rate of change) may be monitored andcompared to a threshold. Based on the comparison, a fuel system leak maybe diagnosed. In some embodiments one or more valves may be positionedin vent 27 and/or purge line 28. The controller 12 may adjust the one ormore valves during leak detection routines.

As described herein, the leak tests performed may be vacuum-based ornegative pressure leak tests. During the negative pressure leak test,canister purge valve 112 and canister vent valve 114 may be kept closedto isolate the fuel system. Vacuum may be applied to the fuel tank orcanister side of the fuel system until a threshold vacuum level has beenreached. Based on a rate of pressure bleed-up (to atmospheric pressure)and a final stabilized fuel system pressure, the presence of a fuelsystem leak may be determined. For example, in response to a bleed-uprate that is faster than a threshold rate, a leak may be determined.

Vehicle system 6 may further include control system 14. Control system14 is shown receiving information from a plurality of sensors 16(various examples of which are described herein) and sending controlsignals to a plurality of actuators 81 (various examples of which aredescribed herein). As one example, sensors 16 may include exhaust gassensor 126 located upstream of the emission control device, temperaturesensor 128, and pressure sensor 129. Other sensors such as additionalpressure, temperature, air/fuel ratio, and composition sensors may becoupled to various locations in the vehicle system 6, as discussed inmore detail in FIG. 2. As another example, the actuators may includefuel injector 66, isolation valve 110, purge valve 112, throttle 62, andthe vacuum pump of ELCM 140. The control system 14 may include acontroller 12. The controller may receive input data from the varioussensors, process the input data, and trigger the actuators in responseto the processed input data based on instruction or code programmedtherein corresponding to one or more routines. Example control routinesare described herein with regard to FIGS. 3-4.

FIG. 2 shows an example embodiment 200 of fuel system 18. As such,vehicle system components previously introduced at FIG. 1 are numberedsimilarly at FIG. 2 and not reintroduced. Turning to example embodiment200 of FIG. 2, canister 22 may receive fuel vapors from fuel tank 20through conduit 31. During regular engine operation, isolation valve 110may be kept closed to limit the amount of diurnal vapors directed tocanister 22 from fuel tank 20. During refueling operations, and selectedpurging conditions, isolation valve 110 may be temporarily opened, e.g.,for a duration, to direct fuel vapors from the fuel tank to canister 22.While the depicted example shows isolation valve 110 positioned alongconduit 31, in alternate embodiments, the isolation valve may be mountedon fuel tank 20.

One or more pressure sensors may be coupled to fuel tank 20 forestimating a fuel tank pressure or vacuum level. While the depictedexample shows pressure sensor 120 coupled to fuel tank 20, in alternateembodiments, the pressure sensor may be coupled between the fuel tankand isolation valve 110. In still other embodiments, a first pressuresensor may be positioned upstream of the isolation valve, while a secondpressure sensor is positioned downstream of the isolation valve, toprovide an estimate of a pressure difference across the valve.

A fuel level sensor 206 located in fuel tank 20 may provide anindication of the fuel level (“Fuel Level Input”) to controller 12. Asdepicted, fuel level sensor 206 may comprise a float connected to avariable resistor. Alternatively, other types of fuel level sensors maybe used. Fuel tank 20 may further include a fuel pump 207 for pumpingfuel to injector 66.

Fuel tank 20 receives fuel via a refueling line 215, which acts as apassageway between the fuel tank 20 and a refueling door 229 on an outerbody of the vehicle. During a fuel tank refueling event, fuel may bepumped into the vehicle from an external source through the refuelingdoor. During a refueling event, isolation valve 110 may be opened toallow refueling vapors to be directed to, and stored in, canister 22.

Fuel vapors released from canister 22, for example during a purgingoperation, may be directed into engine intake manifold 44 via purge line28. The flow of vapors along purge line 28 may be regulated by canisterpurge valve 112, coupled between the fuel vapor canister and the engineintake. The quantity and rate of vapors released by the canister purgevalve may be determined by the duty cycle of an associated canisterpurge valve solenoid (not shown). As such, the duty cycle of thecanister purge valve solenoid may be determined by the vehicle'spowertrain control module (PCM), such as controller 12, responsive toengine operating conditions, including, for example, engine speed-loadconditions, an air-fuel ratio, a canister load, etc. By commanding thecanister purge valve to be closed, the controller may seal the fuelvapor recovery system from the engine intake.

An optional canister check valve 116 may be included in purge line 28 toprevent intake manifold pressure from flowing gases in the oppositedirection of the purge flow. As such, the check valve 116 may benecessary if the canister purge valve control is not accurately timed orthe canister purge valve itself can be forced open by a high intakemanifold pressure. An estimate of the manifold absolute pressure (MAP)may be obtained from MAP sensor 218 coupled to intake manifold 44, andcommunicated with controller 12. Alternatively, MAP may be inferred fromalternate engine operating conditions, such as mass air flow (MAF), asmeasured by a MAF sensor (not shown) coupled to the intake manifold. Thecheck valve may be positioned between the canister purge valve and theintake manifold, or may be positioned before the purge valve.

Canister 22 may communicate with the atmosphere through vent 27. Anevaporative leak check module 140 configured for detecting leaks in fuelsystem 200 may be located in vent 27. In particular, ELCM 140 is coupledin vent 27, between canister 22 and the atmosphere. ELCM 140 includes avacuum pump 202. Vacuum pump 202 may be an electrically-operated vacuumpump driven by an on-board energy storage device (such as battery 52 ofFIG. 1). Vacuum drawn by the pump may be delivered to the fuel systemvia a reference orifice 204. In one example, the reference orifice has asize of 0.017″. ELCM 140 further includes a pressure sensor 209 formonitoring a change in fuel system pressure upon applying a vacuumduring leak detection routines. It will be appreciated, however, thatduring leak detection, fuel system pressure may additionally oralternatively be estimated by a fuel system pressure sensor coupled inconduit 31. This may include, for example, a pressure sensor coupled tofuel tank 20, a pressure sensor coupled between fuel tank 20 andisolation valve 110, a pressure sensor coupled to canister 22, or apressure sensor coupled between canister 22 and isolation valve 110.

During leak detection routines, the vacuum pump 202 may be operated toapply vacuum to the fuel system. Once a threshold vacuum level isreached, vacuum pump operation may be discontinued and a change in fuelsystem pressure may be monitored at the reference orifice 204. Forexample, a change in pressure may be monitored by pressure sensor 209.Based on the change in pressure relative to a threshold, fuel systemleaks may be determined. When a vacuum is being applied by the vacuumpump 202, the isolation valve 110 may be closed (e.g., forced closed bythe vacuum). As such, during leak detection routines, the controller maydetermine the isolation valve 110 is in a known closed position. In someexamples, if a leak is detected, the isolation valve 110 may be stuckopen. As a result, the controller may indicate that the isolation valve110 is degraded.

In other embodiments, the controller 12 may operate the vacuum pump 202to apply vacuum to the fuel system and verify the position of theisolation valve 110. For example, the controller may operate the vacuumpump 202 and verify the position of the isolation valve 110 based onwhether the vacuum pressure is sensed (e.g., actually created) withinthe fuel system. If the vacuum is sensed (e.g., the fuel system pressuredecreases below a vacuum threshold pressure), the controller 12 mayverify that the isolation valve 110 is closed. However, if the vacuum isnot sensed (e.g., not created) during operating the vacuum pump 202, thecontroller 12 may determine that the isolation valve 110 is open.Further details on a method for verifying the position of the isolationvalve 110 is presented at FIG. 4.

The system of FIGS. 1-2 provides for a fuel system comprising an engine,a fuel tank, a canister for storing fuel vapors, a fuel tank isolationvalve (FTIV) coupled in a vapor line between the fuel tank and thecanister, the FTIV held in both opened and closed positions without anyapplied current, and a leak check module including a reference orifice,a vacuum pump, and a pressure sensor. The fuel system further includes acontroller with computer readable instructions for diagnosing a positionof the FTIV based on fuel system pressure and subsequently adjusting theFTIV based on the diagnosed position and engine operating conditions.

In one example, diagnosing the position of the FTIV includes setting aknown position of the FTIV as a closed position when one or more of apressure of the fuel tank increases above a threshold pressure ordecreases below a vacuum threshold pressure. The computer readableinstructions further include instructions for adjusting the vacuum pumpto apply a vacuum to the fuel system in response to a request to operatethe vacuum pump. For example, the request to perform a leak test isgenerated in response to one or more of a first amount of time passingsince diagnosing the position of the FTIV, a second amount of timepassing since performing a leak test, or a fuel system event resultingin uncertainty of the FTIV position.

As described above, the isolation valve (FTIV) may be a bi-stable valveactuated open and closed via an electrical pulse. Without an additionalsensor, the position of the isolation valve may not be known orverified. Thus, if the isolation valve is degraded or in an incorrectposition, there may be no means of discovering the incorrect position.As a result, the isolation valve may not function properly to reduce theamount of fuel vapors absorbed in the canister from the fuel tank.

When a vacuum is sensed in the fuel system, or when a fuel tank pressureincreases above a threshold pressure, the isolation valve may beverified as closed. If the isolation valve were open, vacuum or highpressure in the fuel tank may not be possible. In some cases vacuum orincreased fuel tank pressure may be created in order to diagnose theposition of the isolation valve.

In one example, the vacuum pump of the evaporative leak check module(ELCM) (e.g., ELCM 140 shown in FIGS. 1-2) may apply a vacuum to thefuel system in response to a request to determine the position of theisolation valve and/or a request to perform a leak testing routine. Ifthe fuel system pressure decreases below a vacuum threshold pressure(e.g., a pressure at which vacuum is created) during applying thevacuum, the controller may verify that the isolation valve is closed.Conversely, if the fuel system pressure does not decrease below thevacuum threshold pressure during applying the vacuum, the controller mayverify that the isolation valve is closed. Then, following the isolationvalve position verification, the isolation valve may be actuated asneeded to open or close the valve. If the controller receives a requestto close the isolation valve and the valve is already closed, then thecontroller may not send a signal to the isolation valve to actuate thevalve. Instead, the controller does not send an actuation signal to theisolation valve and the isolation valve remains in the closed position.The controller may then track the position of the isolation valve asactuation signals are sent to the isolation valve.

In another example, the vacuum pump may be used alone to apply vacuum tothe fuel system (e.g., without running a full leak testing routine). Inthis way, the vacuum pump may be operated for a duration, the durationbased on an amount of time required to reach a vacuum pressure thresholdwhich allows for measuring the fuel system and/or fuel tank pressure andverifying the position of the isolation valve. In yet other examples,additional or alternative pumps or system components may create a vacuumor increased fuel tank pressure that may be used for isolation valveposition verification (e.g., diagnosis). For example, increasing ordecreasing temperature may cause the fuel tank pressure to increase ordecrease if the fuel system is closed (e.g., the FTIV is close). Thus,during creation of the vacuum with the system components, the controllermay diagnose the position of the isolation valve.

In this way, an engine method comprises adjusting a fuel tank isolationvalve (FTIV) of a fuel system by sending electrical pulses to the FTIV,counting each of the electrical pulses to track a position of the FTIV,and verifying the position of the FTIV when a vacuum is created in thefuel system. In one example, verifying the position of the FTIV includesverifying that the FTIV is closed when a vacuum is sensed in the fuelsystem. In another example, the method may further comprise verifyingthe FTIV is closed in response to a fuel tank pressure greater than athreshold pressure.

The method further comprises applying a vacuum to the fuel system inresponse to one or more of the position of the FTIV being unknown, aduration since a last FTIV position diagnosis, or a request to run aleak detection routine. In one example, applying a vacuum to the fuelsystem includes operating a vacuum pump coupled to a vent of a canisterof the fuel system. Further, verifying the position of the FTIV includesverifying that the FTIV is open responsive to an expected position ofthe FTIV being an open position and no vacuum being sensed afterapplying the vacuum. Additionally, the method comprises sending anelectrical pulse to actuate the FTIV in response to verifying that theFTIV is open when the expected position of the FTIV is a closedposition. The method may then comprise reapplying the vacuum to the fuelsystem after sending the electrical pulse and indicating degradation ofthe FTIV if no vacuum is sensed after reapplying the vacuum. Forexample, a diagnostic code may be set based on the indication ofdegradation, such code stored in non-transitory memory and readable byan external controller, the code identifying degradation of the FTIVspecifically. Further, as described herein, default action may be taken,via the control system of the vehicle, in response to the indication ofdegradation, including closing one or more valves and generating anindication to the operator that a diagnostic code has been set, such asvia an indicator light, a message on the vehicle message center, etc.

Adjusting the FTIV includes sending one of the electrical pulses toactuate the FTIV from a first position to a desired position. In oneexample, the method includes not sending the one of the electricalpulses to actuate the FTIV when the FTIV is already in the desiredposition. Additionally, the FTIV may be a bi-stable valve coupledbetween a fuel tank and a canister of the fuel system.

Turning now to FIG. 3, a method 300 is shown for adjusting a fuel tankisolation valve (FTIV), such as FTIV 110 shown in FIGS. 1-2. Asdiscussed above, the FTIV may be a bi-stable valve actuated between anopen and a closed position by short electrical pulses sent from thecontroller. With each actuation, the FTIV switches from the closed tothe open position or from the open to the closed position. Instructionsfor executing method 300 may be stored on a memory of a controller (suchas controller 12 shown in FIGS. 1-2) and executed by the controller.

Method 300 begins at 301 by estimating and/or measuring engine operatingconditions. Engine operating conditions may include engine speed andload, fuel tank pressure, fuel system pressure, engine temperatures andpressures, etc. At 302, the method includes counting the electricalpulses sent to the FTIV to track a position of the FTIV. As describedabove, one electrical pulse sent to the FTIV may change the position ofthe FTIV. If the controller knows a starting position of the FTIV (e.g.,after verifying the position of the FTIV as shown at FIG. 4), thecontroller may count each subsequent pulse and update the known (orcurrent) position of the valve in the memory of the controller. Saidanother way, the controller may count and track a number of actuationsof the FTIV to track the current position of the FTIV.

At 303, the method includes determining if a fuel tank pressure isgreater than a threshold pressure or if a fuel system pressure (or fueltank pressure) is less than a vacuum threshold pressure. For example,the vacuum threshold pressure may indicate that a vacuum is beingapplied to the fuel system. If either of the pressure conditions at 303is met, the method continues to 305 to verify the position of the FTIV,as shown at FIG. 4 (described further below). In one example, if vacuumconditions exist in the fuel system or fuel tank pressure is above athreshold pressure, the FTIV may be confirmed as closed. The thresholdpressure may be a fuel tank pressure only attainable if the FTIV isclosed.

If neither of the pressure conditions at 303 ate satisfied, the methodcontinues on to 304. At 304, the method includes determining if theposition of the FTIV (e.g., open or closed) is known. In one example,during running a leak test routine and/or applying a vacuum to the fuelsystem, the controller may verify the position of the FTIV (as shown atFIG. 4). As a result, the position of the FTIV may be known afterconditions of vacuum or high fuel tank pressure in the fuel system.Further, as discussed at 302, the controller may track actuation of theFTIV and track the position of the FTIV from the known (e.g., verified)position. However, during valve operation, the controller may lose trackof the position of the FTIV or an error may occur in the fuel systemcausing the FTIV position to be unknown.

If the FTIV position is not known by the control system (e.g., the FTIVis in an unknown position), the method continues on to 306 to adjust afuel system component and apply a vacuum to the fuel system. As aresult, the position of the FTIV may be verified based on the resultingfuel system pressures. A method for verifying the position of the FTIVis shown at FIG. 4, discussed further below.

Alternatively at 304, if the FTIV position is known, the methodcontinues on to 308 to determine if the known position is the closedposition. If the known position is the closed position, the controllerdetermines the FTIV is closed at 310. At 312, the method includesdetermining if there is a request to open the FTIV. If there is arequest to open the FTIV, the controller sends an electrical pulse tothe FTIV to actuate the FTIV from the closed position to the openposition. As such, the electrical pulse causes the FTIV to switch fromthe closed position to the open position. In one example, a request toopen the FTIV may be generated in response to a refueling event (e.g.,during refueling of the fuel tank via refueling line 215 shown in FIG.2). In another example, a request to open the FTIV may be generated inresponse to purging conditions when a fuel tank pressure increases abovea threshold pressure.

Alternatively at 312, if there is not a request to open the FTIV, thecontroller does not send a pulse to the FTIV and maintains the FTIV inthe closed position at 316. In one example, the controller may receive arequest to close the FTIV. However, since the FTIV is already closed,the controller does not send the electrical pulse to the valve (sincethis would result in opening of the valve). Further, if there is notrequest to open or close the FTIV, the controller maintains the FTIVclosed at 316 by not sending a pulse to actuate the valve.

Returning to 308, if the FTIV is not in the closed position, the methoddetermines the valve is open at 318. At 320, the method includesdetermining if there is a request to close the FTIV. In one example, arequest to close the FTIV may be generated in response to execution of aleak detection routine. In another example, a request to close the FTIVmay be generated following a refueling event or purging event. If thereis a request to close the FTIV, the controller sends an electrical pulseto the FTIV to actuate the FTIV from the open position to the closedposition. However, if there is not a request to close the FTIV, thecontroller does not send an electrical pulse to the FTIV, therebymaintaining the FTIV open at 324. In one example, if the controllerreceives a request to open the FTIV, the controller does not send anelectrical pulse to actuate the FTIV (since this would result in closingof the FTIV). In another example, if the controller does not receive arequest to open or close the FTIV, the controller maintains the FTIVopen by not sending an electrical pulse to actuate the FTIV.

In some embodiments, upon sending a pulse to actuate (e.g., activate)the FTIV open at 314 or closed at 322, the controller may update theknown position to open or closed, respectively. In this way, thecontroller may continuously update the known position of the FTIV withina memory of the controller during FTIV operation.

FIG. 4 shows a method 400 for diagnosing a position of the FTIV.Specifically, method 400 shows determining if the FTIV is in a closed oropen position based on fuel tank pressure and/or vacuum. In one example,vacuum may be created in the fuel system with a vacuum pump. A measuredfuel system pressure during applying the vacuum may verify a position ofthe FTIV and/or determine whether the FTIV is degraded.

The method begins at 402 by estimating and/or measuring engine operatingconditions. Engine operating conditions may include engine speed andload, engine temperatures, fuel tank pressure, fuel system pressure,changes in fuel system pressure, a position of the FTIV, etc. At 404,the method includes determining if a fuel tank pressure is greater thana threshold pressure and/or if a fuel system pressure is less than avacuum threshold pressure. For example, the vacuum threshold pressuremay indicate that a vacuum is being applied to the fuel system. Ifeither of the pressure conditions at 404 is met, the method continues onto 406 to determine that the FTIV is closed and set the known positionof the FTIV as the closed position. Regular FTIV operation may continue,as shown at FIG. 3. When a vacuum is applied to the fuel system, theresulting vacuum pressure may only be attainable if the FTIV is closed.Otherwise, if the FTIV is open, the measured fuel system pressure maynot be less than the vacuum threshold pressure. As such, during vacuumor high fuel tank pressure conditions, the controller may determine thatthe FTIV is in the closed position. This known position may then be usedto adjust the FTIV into requested (e.g., desired) positions, as shown atFIG. 3.

However, if there is not a vacuum applied to the fuel system or a highfuel tank pressure, the method continues on to 408 to determine whetherfuel tank degradation is present. For example, if a component of thefuel tank is degraded, a diagnostic code may be generated by thecontroller. If an error or diagnostic code is present, the controllermay be unable to detect and diagnose the FTIV position. As a result, themethod waits for the error or code to clear (e.g., resolve) and returnsat 410. However, if no codes or degradation of the fuel tank is present,the method continues on to 412 to determine if there is a request tooperate the vacuum pump. In alternate embodiments, the method at 412 mayinclude determining if there is a request to apply a vacuum to the fuelsystem by another means (e.g., with an alternate pump or fuel systemcomponent) or if there is a request to increase the fuel tank pressureabove the threshold pressure using a fuel system component (such as apump or valve).

Entry conditions for vacuum pump operation may include a variety ofengine and/or fuel system operating conditions and parameters. In oneexample, entry conditions for vacuum pump operation may include anamount of time since a prior leak testing routine. For example, leaktesting may be performed on a set schedule, e.g. leak detection may beperformed after a vehicle has traveled a certain amount of miles since aprevious leak test or after a certain duration has passed since aprevious leak test. As discussed above, running the leak testing routineincludes operating the vacuum pump. In another example, entry conditionsfor vacuum pump operation may include an amount of time since diagnosingthe position of the FTIV. Alternatively or additionally, vacuum pumpoperation may be performed after a fuel system or engine event occursresulting in uncertainty of the FTIV position. In yet another example,vacuum pump operation may occur when turning the vehicle on or off, orafter an event where the FTIV is commanded into the closed position ifposition verification is requested. As a result, the controller may notknow whether the FTIV is open or closed.

If there is not a request to operation the vacuum pump, the methodcontinues on to 414 to not operate the vacuum pump and instead use thelast known position of the FTIV to adjust the FTIV, as shown at FIG. 3.However, if there is a request to operate the vacuum pump (or run a leaktest), the method continues on to 416 to apply a vacuum to the fuelsystem. As described above, applying the vacuum to the fuel system mayinclude operating the vacuum pump of an evaporative leak check module(ELCM) positioned in the fuel system (such as ELCM 140 shown in FIGS.1-2). The method at 416 may include operating the vacuum pump (oralternate fuel system component) for a duration. The duration may bebased on an amount of time needed for the fuel system pressure todecrease below the vacuum threshold pressure and allow the controller toverify that the FTIV is closed. At 418, the method includes determiningif the vacuum pressure is sensed. In one example, a pressure sensor inthe fuel system may sense the fuel system pressure. If the vacuumpressure is detected, the FTIV may be closed. As a result, thecontroller may set the know position of the FTIV to closed at 406.However, if the vacuum is not detected (e.g., the fuel system pressuredoes not decrease to or below the vacuum threshold pressure), the methodcontinues on to 419 to determine that the FTIV is open. In someembodiments, method 300 may end at 419 and then continue FTIV operation.

However, in alternate embodiments, as shown in FIG. 4, the methodcontinues on to determine if the FTIV is stuck open and degraded. Forexample, if the expected position of the FTIV is the closed position (asdetermined based on valve position tracking), the method may continue to420 to determine if the FTIV is degraded and/or reset the known positionof the valve. At 420 to the method includes determining if the FTIV opendetection is the first detection. If the detection is the firstdetection, the controller sends an electrical pulse to the FTIV toactuate the valve at 422. Actuating the FTIV may help to unstick thevalve if it is stuck open. The method returns to 416 to apply the vacuumagain. If the FTIV open detection is not the first detection (e.g., thecontroller has already attempted to unstick the valve via actuation),the method continues on to 424 to determine the FTIV is degraded (andpossibly stuck in an open position). The method at 424 may includenotifying a vehicle operator the degradation.

Method 400 includes applying a vacuum to the fuel system with an ELCM todiagnose the position of the FTIV. Specifically, applying a vacuum tothe fuel system with the vacuum pump of the ELCM and then detecting thevacuum via measuring the fuel system pressure may indicate the FTIV isclosed. Following the operation of the vacuum pump and verification ofthe FTIV position, the position of the FTIV may be known and updated inthe memory of the controller and used for subsequent FTIV adjustments asrequired based on engine operating conditions. However, in alternateembodiments, method 400 may include adjusting alternate fuel systemcomponents to create a vacuum or high pressure in the fuel tank that maybe used to verify the position of the FTIV. For example, an additionalor alternative pump may be positioned within the fuel system and createincreased pressure in the fuel tank.

FIG. 5 shows a graphical example of adjustments to the FTIV resultingfrom changes in fuel system pressures. Specifically, graph 500 showschanges in a position of the FTIV at plot 502, changes in fuel tankpressure at 504, changes in operation of a vacuum pump at plot 506,changes in fuel system pressure at plot 508. As described above, in oneexample, the vacuum pump may be part of an evaporative leak check module(ELCM) positioned in the fuel system. Operating the vacuum pump maycreate a vacuum, thereby causing a decrease in fuel system pressure andindicating that the FTIV is closed. In other embodiments, an alternativeor additional fuel system component may be used to apply a vacuum to thefuel system or increase the fuel tank pressure above a thresholdpressure, thereby allowing diagnosis of the FTIV position.

Prior to time t1, the FTIV may be open. At time t1, entry conditions foroperating the vacuum pump may be met. As a result, the controller mayoperate the vacuum pump (plot 506). However, after time t1, the fuelsystem pressure may not decrease below the vacuum threshold pressure T1(plot 508). As a result, the controller may indicate the FTIV is open.However, the expected position of the FTIV may be the closed position.Thus, the controller may actuate the FTIV in order to unstick or resetthe valve position. In response to the actuation, the FTIV may closebetween time t1 and time t2. After actuating the FTIV, the controllermay continue operating the vacuum pump in order to verify that the FTIVclosed. In some embodiments, the controller may operate the vacuum pumpat time t1 responsive to a duration passing since last determining theposition of the FTIV. In another example, the vacuum pump may be turnedon at time t1 in response to the FTIV position not being known.

At time t2 the vacuum pump is turned off (after verifying the FTIV isclosed). At time t3, the controller may send an electrical pulse to theFTIV to open the FTIV in response to engine operating conditions (plot502). In one example, the controller may actuate the FTIV open during arefueling event. At time t4, the controller may actuate the FTIV toclose (plot 502) by sending an electrical pulse to the FTIV (e.g., inresponse to the conclusion of the refueling event).

At time t6, the controller may receive a request to operate the vacuumpump. As a result, the controller may activate the vacuum pump at timet6 (plot 506). As a result, the fuel system pressure decreases below thevacuum threshold pressure T1 (plot 508). Thus, the FTIV is verified asbeing in the closed position. The vacuum pump is turned off at time t7,after running for a duration. As described above, the duration may belong enough for the fuel system pressure to decrease below the vacuumthreshold pressure T1 and verify that the FTIV is closed.

As shown in FIG. 5, a method for an engine fuel system may includetracking a position of a fuel tank isolation valve (FTIV). During afirst condition (as show at times t3 and t4) when a position of the FTIVis known, the method may include adjusting the position of the FTIVbased on engine operating conditions from the known position. During asecond condition (as shown at time t1 and time t6) when the position ofthe FTIV is not known, the method may include applying a vacuum to thefuel system and verifying the position of the FTIV based on detection ofthe vacuum.

In one example, applying the vacuum includes operating a vacuum pump ofan evaporative leak check module positioned in the fuel system. In oneexample, verifying the position of the FTIV includes, after applying thevacuum, verifying the FTIV is close in response to the fuel systempressure being less than the vacuum threshold pressure (as shown aftertime t6) and verifying the FTIV is open in response to the fuel systempressure being greater than the vacuum threshold pressure (as shownafter time t1). As shown at time t3, after moving the FTIV to a closedposition, the method may include sending an electrical pulse to actuatethe FTIV into an open position, from the closed position, in response toa request to open the FTIV. In another example, after moving the FTIV toa closed position, the method may include not sending an electricalpulse to actuate the FTIV in response to a request to close the FTIV.

The method may include adjusting the FTIV into an open position duringone or more of refueling events or during purging events wherein a fueltank pressure increases above a threshold pressure and adjusting theFTIV into the closed position during leak detection routines. In oneexample, adjusting the FTIV includes sending an electrical pulse toactuate the FTIV and tracking the position of the FTIV includes countinga number of actuations of the FTIV and updating the known position aftereach actuation.

In this way, a position of a fuel tank isolation valve (FTIV) may bediagnosed. Specifically, the position of a bi-stable FTIV may bevalidated by applying a vacuum to the fuel system or increasing a fueltank pressure over a threshold pressure. The vacuum and/or the thresholdpressure may be pressures that may only be attainable when the FTIV isclosed, thereby verifying the closed position of the FTIV during thesepressure conditions. Thus, when a vacuum is applied to the fuel systemor the fuel tank pressure increases above the threshold pressure, theFTIV position may be confirmed as closed. This known closed position maythen be used by the controller for subsequent FTIV adjustments. In oneexample, the vacuum may be created with a vacuum pump of an evaporativeleak check module (ELCM) during a leak testing routine. In this way, atechnical effect is achieved by adjusting a fuel system component andverifying the FTIV position based on resulting fuel system pressures,thereby increasing the accuracy of subsequent FTIV control.

As another embodiment, applying a vacuum to the fuel system (orincreasing the fuel tank pressure above the threshold pressure) mayforce the FTIV to close. As a result, the FTIV position may be confirmedas closed after operating the vacuum pump and/or running a leakdetection routine wherein the vacuum pump is used to create a vacuum inthe fuel system. For example, an engine method may include adjusting afuel system component to move a fuel tank isolation valve (FTIV) of afuel system to a known position. The method further comprises duringsubsequent engine operation, adjusting the FTIV to a desired positionafter it is moved to the known position. In one example, the knownposition is a closed position. Further, adjusting the FTIV to thedesired position after it is moved to the known position may furtherinclude adjusting the FTIV based on the FTIV being in the known positionand based on a request to move the FTIV to a new position, the newposition being different than the known position. The method may furthercomprise setting the known position of the FTIV as the closed positionwhen one or more of a fuel tank pressure increases above a thresholdpressure or decreases below a vacuum threshold pressure. As one example,the FTIV is a bi-stable valve coupled between a fuel tank and a canisterof the fuel system.

In one example, adjusting the FTIV to the desired position includessending an electrical pulse to actuate the FTIV from a first position tothe desired position. In another example, the method further includesnot sending the electrical pulse to actuate the FTIV when the FTIV isalready in the desired position. The method may further include trackinga number of actuations of the FTIV after moving the FTIV into the knownposition and updating the known position after each actuation.

In one example, adjusting the fuel system component includes operating avacuum pump to apply a vacuum to the fuel system, the vacuum pumpcoupled to a vent of a canister of the fuel system. The method mayfurther include turning off the vacuum pump and monitoring a change infuel system pressure following the applying of the vacuum to the fuelsystem relative to a threshold. Additionally, the method may includeindicating degradation of the FTIV when the change in fuel systempressure is greater than the threshold.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory. The specific routinesdescribed herein may represent one or more of any number of processingstrategies such as event-driven, interrupt-driven, multi-tasking,multi-threading, and the like. As such, various actions, operations,and/or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedactions, operations and/or functions may be repeatedly performeddepending on the particular strategy being used. Further, the describedactions, operations and/or functions may graphically represent code tobe programmed into non-transitory memory of the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. An engine method, comprising: via acontroller: adjusting a fuel tank isolation valve (FTIV) of a fuelsystem by sending electrical pulses to the FTIV; counting each of theelectrical pulses to track a position of the FTIV; applying a vacuum toforce the FTIV to a known closed position; verifying the closed positionof the FTIV in response to sensing the applied vacuum in the fuelsystem; and following verification, actuating the FTIV to a desiredposition based on the verified position and engine operating conditionsby sending further electrical pulses.
 2. The method of claim 1, furthercomprising generating an indication of the verified position, the methodfurther comprising taking a default action in response to the indicationof the verified position.
 3. The method of claim 1, further comprisingverifying the FTIV is closed in response to a fuel tank pressure greaterthan a threshold pressure.
 4. The method of claim 1, further comprisingapplying the vacuum to the fuel system in response to one or more of theposition of the FTIV being unknown, a duration since a last FTIVposition diagnosis, or a request to run a leak detection routine.
 5. Themethod of claim 4, wherein applying the vacuum to the fuel systemincludes operating a vacuum pump coupled to a vent of a canister of thefuel system to apply a negative pressure to the fuel system.
 6. Themethod of claim 4, wherein verifying the closed position of the FTIVincludes verifying that the FTIV is open responsive to an expectedposition of the FTIV being an open position and no vacuum being sensedafter applying the vacuum.
 7. The method of claim 6, further comprisingsending an electrical pulse to actuate the FTIV in response to verifyingthat the FTIV is open when the expected position of the FTIV is theclosed position.
 8. The method of claim 6, further comprising reapplyingthe vacuum to the fuel system after sending the electrical pulse andindicating degradation of the FTIV if no vacuum is sensed afterreapplying the vacuum.
 9. The method of claim 1, wherein adjusting theFTIV includes sending one of the electrical pulses to actuate the FTIVfrom a first position to the desired position.
 10. The method of claim9, further comprising not sending the one of the electrical pulses toactuate the FTIV when the FTIV is already in the desired position. 11.The method of claim 1, wherein the FTIV is a bi-stable valve coupledbetween a fuel tank and a canister of the fuel system and whereinverifying the closed position includes verifying the closed position ofthe FTIV in response to sensing fuel system pressure decreasing below avacuum threshold pressure, where the vacuum threshold pressure is apressure at which vacuum is created.
 12. A method for an engine fuelsystem, comprising: via a controller: tracking a position of a fuel tankisolation valve (FTIV); and during a first condition when the positionof the FTIV is known, adjusting the position of the FTIV based on engineoperating conditions from the known position; and during a secondcondition when the position of the FTIV is unknown, applying a vacuum tothe engine fuel system and the FTIV to force the FTIV to a known closedposition and verifying the closed position of the FTIV based ondetection of the vacuum.
 13. The method of claim 12, wherein applyingthe vacuum includes operating a vacuum pump of an evaporative leak checkmodule positioned in the engine fuel system to create the vacuum. 14.The method of claim 12, wherein verifying the closed position of theFTIV includes, after applying the vacuum, verifying the FTIV is closedin response to an engine fuel system pressure being less than a vacuumthreshold pressure and verifying the FTIV is open in response to theengine fuel system pressure being greater than the vacuum thresholdpressure.
 15. The method of claim 12, further comprising, after movingthe FTIV to the closed position, sending an electrical pulse to actuatethe FTIV into an open position, from the closed position, in response toa request to open the FTIV; and not sending an electrical pulse toactuate the FTIV in response to a request to close the FTIV.
 16. Themethod of claim 12, further comprising adjusting the FTIV into an openposition during one or more of refueling events or during purging eventswherein a fuel tank pressure increases above a threshold pressure andadjusting the FTIV into the closed position during leak detectionroutines.
 17. The method of claim 12, wherein adjusting the FTIVincludes sending an electrical pulse to actuate the FTIV and whereintracking the position of the FTIV includes counting a number ofactuations of the FTIV and updating the known position after eachactuation.
 18. A fuel system, comprising: an engine; a fuel tank; acanister for storing fuel vapors; a fuel tank isolation valve (FTIV)coupled in a vapor line between the fuel tank and the canister, the FTIVheld in both opened and closed positions without any applied current; aleak check module including a reference orifice, a vacuum pump, and apressure sensor; and a controller with computer readable instructionsfor: applying a vacuum to the fuel system via the vacuum pump to forcethe FTIV to a known closed position; and diagnosing the closed positionof the FTIV based on fuel system pressure after applying the vacuum andsubsequently adjusting the FTIV based on the diagnosed position andengine operating conditions.
 19. The system of claim 18, whereindiagnosing the closed position of the FTIV includes setting a knownposition of the FTIV as the closed position when one or more of apressure of the fuel tank increases above a threshold pressure ordecreases below a vacuum threshold pressure.
 20. The system of claim 18,wherein the computer readable instructions further include instructionsfor adjusting the vacuum pump to apply the vacuum to the fuel system inresponse to a request to operate the vacuum pump and wherein the requestto operate the vacuum pump is generated in response to one or more of afirst amount of time passing since diagnosing the closed position of theFTIV, a second amount of time passing since performing a leak test, or afuel system event resulting in uncertainty of the FTIV position.